Magma stored under volcanoes is mostly solid reports that most of a volcano’s magma probably isn’t the oozing, red-hot molten goo often imagined. Analyses of zircon crystals, spewed from a volcanic eruption in New Zealand, show that the crystals spent the vast majority of their time underground in solid, not liquid, magma, researchers report in the June 16 Science. The results suggest the magma melted shortly before the volcano erupted.

This finding helps confirm geologists’ emerging picture of magma reservoirs as mostly solid masses, says geologist John Pallister of the U.S. Geological Survey in Vancouver, Wash., who was not involved in the study. And it could help scientists more accurately forecast when volcanoes are poised to erupt.